The invention relates to a method for manufacturing rectangular lids, with tear tabs at the ends of the lids, from a foil web in which an incision is cut through to the edge of the foil in at least one of the two long edges, then the areas of foil on both sides of the incision are folded back on themselves along fold lines to form the tear tabs and the foil web is cut-off to form the lids.
The invention also concerns a device for manufacturing square lids with tear tabs at the corners of the lids from a foil web using a frame in which the foil is held, at least one cutting device for cutting an incision through to the edge of the foil in at least one of the two longitudinal edges of the foil, as well as a folding device with a folding tool and a cut-off device for cutting the foil web into lengths to form the lids; the folding tool moves back and forth between a starting position located on one side of the foil web and an end position on the other side of the foil web, and as it moves if folds back on themselves the areas of foil on both sides of the cutting plane to form the tear tabs which are at least partially held down by the folding tool when it reaches its end position.
A procedure and device of the type mentioned at the beginning are known from German Patent DE-PS No. 15 86 221. This patent describes a machine for closing filled containers, such as TV dinner trays, with lids, which are also produced with this machine. For this purpose, a web of, for example, aluminium or plastic foil is paid out from a roll and runs stepwise through a device for manufacturing the lids. This device consists of a sequential arrangement of a cutting station, folding station, and a cut-off station for cutting off the lids. Then the lids are fed to a sealing station where the containers are sealed shut. Each container is provided with an outwards extending flange. After being placed on the container the lid is crimped down and around this flange. The dimensions of the tear tabs extending over the entire length of the narrow sides of the container are such that after the lid has been crimped on, the free end sections of the tabs are arranged on the upper side of the lid where they are thus easy to take hold of.
Each lid is folded upwards over the entire length of and parallel to one of its short sides, as formed by the longitudinal edges of the foil web, and two incisions through to the edge of the lid and arranged at a certain distance apart are cut in it. The lid thus possesses three tear tabs by means of which it can be easily and completely detached from the container in three strips extending over the total width of the short end of the container.
The incisions are cut at the cutting station during the stationary phase between two steps in the advance of the foil web by means of two cutting devices arranged at a certain spacing from each other in the form of paired knives. The amount of advance between two stationary phases corresponds to the length of the three tear strips.
On the next advance the foil web which is incised in this manner is fed to the folding station in which the areas of foil between the incisions are folded by a folding tool of appropriate length.
In the following cut-off station the sections of foil are cut-off between two incisions so that a lid is formed with two tear tabs arranged at the corners of the lid and a tear tab in the middle between them.
The production of lids according to this known procedure requires relatively complex, precisely mutually adjusted devices that take up a lot of space. Just to form the tear tabs it requires two knives spaced a certain distance apart and a separate folding station whose operating elements are exactly adjusted to the knives, as well as a cut-off station. The length of each station requires its own drive.
A further disadvantage is the fact that a relatively large number of incisions per lid has to be cut and the corresponding foil areas have to be folded. The additional consumption of foil material is also correspondingly large in comparison with the area of the lid.
The conversion of the system to lids or tear tabs of different dimensions can be carried out only in a special workshop because not only the knives in the cutting station and the folding tool in the folding station have to be readjusted to the new dimensions, but also both stations must be adjusted relative to each other and to the cut-off station to take account of the new feed rate.
It is the purpose of the invention to further develop a method and a device of the kind mentioned at the beginning in such a way that the lids can be manufactured without impairing their tear-off properties with little design-related and procedural effort.